The semiconductor integrated circuit (IC) industry has experienced exponential growth. Technological advances in IC materials and design have produced generations of ICs where each generation has generally smaller and more complex circuits than the previous generation. This scaling down process generally provides benefits by increasing production efficiency and lowering associated costs. Such scaling down has also increased the complexity of processing and manufacturing ICs.
For example, in certain ICs it is common to have both small and large features on the same chip. One example is CMOS image sensors. A logic area in a CMOS image sensor may include transistor features as small as few tens of nanometers (nm), while a sensing area of the CMOS image sensor may include light sensitive regions or light blocking regions as large as few tens of microns (μm). Another example is biochips which may include openings (or windows) for receiving large DNA samples as well as processing circuitry that are made of nano-sized circuit features. When manufacturing these types of chips, measuring critical dimension (CD) of the circuit features, both large and small, is quite challenging because typical CD measurement tools (e.g., wafer metrology tools) are incapable of measuring both large and small features with acceptable accuracy. For example, many wafer metrology tools specify an upper limit of the target (to-be-measured) CD, beyond which the measurement accuracy is not guaranteed. The upper limit may be only few microns or less. Further, even within the upper limit, the measurement accuracy may be only guaranteed to be within few percentages, such as 1%. For a circuit feature as large as 10 μm, the CD measurement inaccuracy (or error) could be 100 nm or more, which could be unacceptable considering that nearby circuit features only have CDs in tens of nanometers. Maintaining the spatial relationship between these large and small features during IC manufacturing would become very difficult with the large CD measurement errors.
Improvements in these areas are desired.